<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .parent {
            width: 200px;
            height: 200px;
            background-color: gray;
        }

        .son {
            width: 50px;
            height: 50px;
            background-color: red;
            border-radius: 25%;
        }
    </style>
</head>

<body>
    <p>
        撒大苏打阿达萨达啊实打实的撒大苏打阿达萨达啊实打实的撒大苏打阿达萨达啊实打实的撒大苏打阿达萨达啊实打实的撒大苏打阿达萨达啊实打实的撒大苏打阿达萨达啊实打实的撒大苏打阿达萨达啊实打实的撒大苏打阿达萨达啊实打实的撒大苏打阿达萨达啊实打实的撒大苏打阿达萨达啊实打实的
    </p>

    <div>
        撒大苏打阿达萨达啊实打实的撒大苏打阿达萨达啊实打实的撒大苏打阿达萨达啊实打实的撒大苏打阿达萨达啊实打实的撒大苏打阿达萨达啊实打实的撒大苏打阿达萨达啊实打实的撒大苏打阿达萨达啊实打实的撒大苏打阿达萨达啊实打实的撒大苏打阿达萨达啊实打实的撒大苏打阿达萨达啊实打实的
    </div>

    <div class="parent">

        <div class="son">

        </div>
    </div>
</body>

</html>